1. Field of the Invention
The present invention relates to an intake flow control device having a valve unit for changing intake flow so as to switch air flow formed in a combustion chamber of an internal combustion engine.
2. Description of Related Art
As shown in FIG. 6, an intake flow control device 100 includes an intake manifold 102 defining an intake passage 103 therein. A valve unit 104 is arranged in the intake passage 103 to change intake flow. Air flow to be formed in a combustion chamber 111 of an internal combustion engine 112 is changed by controlling the valve unit 104 to open or close the intake passage 103.
When the engine 112 is cool, or when the amount of intake air is small, the valve unit 104 totally closes the intake passage 103 so as to generate a tumble flow in response to a control signal output from an electronic control unit (ECU, not shown) of the engine 112. A turbulence generated in the combustion chamber 111 is enhanced so as to homogenize a fuel-air mixture. A combustion generated in the combustion chamber 111 is improved so as to increase combustion efficiency and decrease emission of exhaust gas.
In contrast, when the engine 112 is warm, a large amount of intake air is necessary. In this case, the valve unit 104 totally opens the intake passage 103 so as to stop generating the tumble flow. Thus, all intake air is made to pass through the intake passage 103.
As shown in FIGS. 7A and 7B, JP-A-2007-170340 (corresponding to US 2007/0144483 A1) discloses an intake flow control device having a valve unit 104 constructed with a valve 109, a valve shaft 105, and a housing 108. The valve 109 is rotatably arranged in an intake passage 103 so as to generate a tumble flow to be supplied into a combustion chamber. The intake passage 103 is closed by the valve 109 so as to decrease a cross-sectional area of the intake passage 103. The tumble flow is generated by opening or closing the valve 109.
The valve 109 is mainly made of resin, and is integrally connected to the valve shaft 105. The valve 109 is a swing-type valve, and the valve shaft 105 is supported by two side walls of the housing 108 defining the intake passage 103 therein. When the valve 109 closes the intake passage 103, the valve 109 is approximately perpendicular to the intake passage 103.
The housing 108 has an outer wall, which is held in an intake manifold 102 through a floating gasket 110. Thus, thermal deformation of the housing 108 due to a temperature change can be absorbed by the floating gasket 110. The valve 109 and the housing 108 oppose to each other with a predetermined side clearance C. Intake flow is separated into a main flow M and a bypass flow B at the valve unit 104. The amount of the bypass flow B is determined by the side clearance C. The tumble flow can be easily generated by controlling the side clearance C, and the amount of the main flow M can be maintained by controlling the side clearance C.
The valve unit 104 is inserted into each branch tube of the intake manifold 102. The number of the valve units 104 corresponds to the number of cylinders of the engine. A drive shaft having a rectangular cross-section penetrates and connects the valve shafts 105 of the valve units 104, which are arranged in a line. An actuator is directly connected to the drive shaft. The valve unit 104 can be driven to open or close the intake passage 103 due to the drive shaft and the actuator.
When the valve unit 104 totally closes the intake passage 103, intake air is contracted by the valve unit 104. A flowing area of the contracted air is set to be small so as to generate a high tumble flow. A speed of the contracted air becomes fast, and a turbulence is enhanced so that the high tumble flow can be generated. However, if air flowing in the intake passage 103 is more contracted, a flow loss is increased when the valve unit 104 totally closes the intake passage 103. Further, the bypass flow B flowing through the side clearance C is increased, because the flow loss is increased. Furthermore, the amount of the main flow M may be decreased. Thereby, the high tumble flow cannot be increased.
The side clearance C is made small so as to secure the generation of the high tumble flow. Thus, the amount of bypass flow B is decreased, and a predetermined amount of main flow M is secured. However, the floating gasket 110 absorbing the thermal deformation of the housing 108 is required so as to prevent a break of the valve 109 when the side clearance C is made small. In this case, cost may be increased because the floating gasket 110 is additionally needed.
The housing 108 of the valve unit 104 is supported by the floating gasket 110. When a pulsing of air flow is generated in the intake passage 103, the housing 108 may be rotated in a condition that the valve shaft 105 is a center of the rotation. In this case, the valve unit 104 may contact with other parts with slapping sound. When an additional construction change or a sound-absorbing material is needed for reducing the slapping sound, a cost of producing the intake flow control device may be increased.
Further, the valve 109 may contact the housing 108 due to a thermal deformation or a time-lapse deposit adherence. When the valve 109 contacts the housing 108, the valve 109 cannot smoothly rotate. Further, the rotation of the valve 109 may be stopped. In this case, a drive torque of the actuator may be increased, such that a size of the actuator needs to be increased. Thus, the cost of producing the intake flow control device may further be increased.
If the side clearance C is made large, the break of the valve 109 and the contact between the valve 109 and the housing 108 due to the time-lapse deposit adherence can be prevented. Further, the floating gasket 110, and the increasing of the size of the actuator are not needed, such that the cost of producing the intake flow control device may not be increased.
Furthermore, a predetermined amount of the main flow M and the high tumble flow are required to be maintained without the increasing of the bypass flow B, even if the side clearance C is made large.